1. Field of the Invention
This invention relates to a seed supplying mechanism for seed coating apparatus that coat seeds with a gel containing nutrients, sterilizers or the like and having elastic properties.
2. Description of the Prior Art
It is conventionally general that seeds are sowed without coating. However, in order to protect seeds from being eaten by animals or to subject seeds to preliminary processing for improvement in sterilization and germination, coating has been employed.
A seed is conventionally coated with clay, fine sand or a mixture of clay or fine sand with sugar adhered to the periphery of the seed by means of a binder such as CMC (carboxymethyl cellulose) sprayed. A sterilizing or oxygen-generating agent may be included in the coating material.
The coating obtained in these examples is relatively of a hard nature, but a seed may be covered with a gel or gelatin-like material that swells on containing water to provide soft coating.
In the conventional coating technique, however, there are found no examples in which seeds are coated with an aqueous gel that cures only a surface of the coating layer.
To realize the above, there has been developed a seed coating apparatus and is disclosed, e.g. in Japanese UM application Laid-Open Specifications Nos. Hei 5-7015 and Hei 5-7016, in which a seed is dropped and supplied to a layer of gel and enclosed therein when the gel is sphericalizod.
The seed coating apparatus includes a gel discharging mechanism and a seed supplying mechanism, and when a gelatinizing agent is discharged from a nozzle in the gel discharging mechanism and forms a layer below the nozzle which gradually droops by its own weight, the seed supplying mechanism drops a seed to the layer from above so that it is held in the drooping layer.
On subsequent supply of the gelatinizing agent from the nozzle, a gel layer is formed in which the seed and air are sealed. The gel layer gravitationally drops when it no longer can sustain its own weight and is supplied to a curing liquid in a curing vessel while sphericalizod during its falling.
An outline of the gel discharging mechanism will be given below. The gel discharging mechanism B, as shown in FIG. 6, includes a valve main body 1 rectangular in cross-section in which is formed an open portion 2 in communication with a gel pressurizing plunger (not shown). A pipeway 42 (FIG. 1) extends from an opening 3 at the lower end of the valve main body 1 to a coating material storing tank 41 between the opening 3 and the open portion 2 is arranged a check valve-constituting steel ball 4 to open and close the opening 3; and a valve casing 5 is mounted at the left side of the valve main body 1.
The valve casing 5 has a plunger insertion hole 6 vertically extending therethrough, at the lower end of which is formed a valve seat 6a. A bush 7 is fitted inside the plunger insertion hole 6 and in the the bush 7 is vertically movably inserted a hollow nozzle plunger 8. The nozzle plunger 8 has at the lower half thereof an outer periphery reduced in diameter to provide a pressure receiving surface 8a.
A gel flow channel 9 is provided to communicate the plunger insertion hole 6 and the open portion 2, so that the gel fed from the coating material storing tank to the open portion 2 via the opening 3 and the check valve 4 fills the gel flow channel 9 and the plunger insertion hole 6.
At its upper end the valve casing 5 is provided with a cylindrical portion 10 with a hollow interior in alignment with the plunger insertion hole 6. The cylindrical portion 10 is at its outer periphery formed with a male screw 10a, so that a spring adjuster 11 with a corresponding female screw 11a formed on its inner periphery is threaded over the male screw 10a. A spring receiver 12 is mounted on the nozzle plunger 8, and a spring 13 is interposed between the spring receiver 12 and the spring adjuster 11 to urge the nozzle plunger 8 downwardly.
The lower end of the nozzle plunger 8 is thus normally seated on a valve seat 6a to close the valve. As the gel pressurizing plunger is moved so as to pressurize the gel inside the gel flow channel 9, the gel presses the pressure receiving surface 8a to move the nozzle plunger 8 upwardly and open the valve, thereby causing the gel to be discharged from below the nozzle plunger 8.
As the gel pressurizing plunger is moved back and the pressure on the gel in the gel flow channel 9 is reduced, the nozzle plunger 8 is urged downwardly by the spring 13 to close the valve, while causing the gel to be supplied from the check valve.
As the nozzle plunger 8 is lowered to close the valve, the discharge of the gel is stopped, while at the same time the gel that remains at the underside of the valve seat forms a gel layer below the plunger insertion hole 6, which gradually droops by its own weight.
Concurrently, a seed is dropped from an above-located seed supply apparatus onto the gel layer so that the seed is enclosed together with a bubble in the drooping gel layer. The gel supplied on subsequent opening of the valve covers top of the drooping gel layer. As a result, the gel layer that can no longer sustain its own weight drops gravitationally to a curing vessel (not shown) while sphericalized due to the surface tension during falling.
Conventional seed supply apparatuses include an apparatus of the type in which an aperture is perforated through a hollow rotary drum to vacuum-attract a seed when the pressure inside the rotary drum is made negative, and an apparatus of the type in which a suction tip is employed to vacuum-attract a seed from a seed-containing vessel.
In the conventional seed supply apparatus of the suction tip type, at an end of a rotary arm rotatably driven by a rotary actuator is provided a hollow suction tip having a tapered end, with the tapered end directed downwardly. When rotation of the rotary arm is stopped, a seed vessel containing a large number of seeds is moved upwardly towards the suction tip to allow the same to vacuum-attract a seed therefrom. When a seed is confirmed attracted, the seed vessel is lowered and the rotary arm is rotated to position the suction tip just above the gel discharging mechanism, followed by supplying an air pressure to the suction tip and causing the suction tip to drop the seed through the nozzle plunger in the gel discharging mechanism to the gel layer.
The seed coating apparatus of the suction tip type has the following drawbacks:
1) There is a limitation to the size of the seed vessel that carries seeds and moves upwardly and downwardly. As the number of seeds in the seed vessel is gradually reduced, it becomes more likely that the suction tip makes errors in sucking seeds, making it necessary that the suction tip retries attracting each time. Consequently, the capability of the seed coating apparatus is lowered. PA1 2) To solve the above drawback, it is necessary to provide a device that automatically supplies seeds and prevent a reduction in the number of seeds contained in the seed vessel. This solution, however, has the following drawbacks:
Likewise, when seeds are added in the seed vessel in large numbers, it is likely that a plurality of seeds sucked to the suction tip interfere with each other to cause an error in vacuum-attracting.
i) Seeds are different in volume and mass depending on the kind of seeds, and thus each time the seeds to be coated are changed, the automatic seed supplying device must be largely adjusted accordingly. PA2 ii) It is difficult to automatically supply seeds to the seed vessel repeatedly moved upwardly and downwardly. PA2 iii) The automatic seed supplying device has a complicated structure and leads to a high production cost.